This invention relates to a radio paging receiver which is capable of informing a possessor of reception of a call number signal assigned to the radio paging receiver. It is to be noted throughout the instant specification that this invention is applicable not only to a radio paging receiver with a display unit but also to a radio paging receiver without any display unit, although description will be restricted to the radio paging receiver with the display unit.
A conventional radio paging receiver of the type described is operable in response to a radio signal modulated by a paging signal or a call number signal and a display information signal or a message signal displayed on a display unit. In general, such a paging signal and a display information signal is preceded by a preamble signal composed of repetitions of a logic "1" level signal and a logic "0" level signal.
In the radio paging receiver, the radio signal is received as a reception signal and demodulated by a receiver unit into a sequence of digital signals which is delivered to a decoder unit. The decoder unit detects whether or not the call number signal included in the digital signals is coincident with a preassigned call number signal. On detection of coincidence between the call number signal and the preassigned call number signal, a loudspeaker and a display unit are energized to generate an audible tone and to display the display information signal.
In order to correctly carry out the above-mentioned processing in the decoder unit, a sequence of internal clock pulses which is synchronized with the digital signal sequence should be reproduced within the radio paging receiver. To this end, a clock synchronization circuit is included in the radio paging receiver. In the clock synchronization circuit, synchronization control operation is carried out only during reception of the preamble signal and is finished after the preamble signal. Therefore, the internal clock synchronization pulses are autonomously generated in the radio paging receiver after the synchronization control operation.
With this structure, it often happens that the internal clock pulses are disordered from the digital signal for some reason and are put into an asynchronous state. In this event, synchronization can be neither controlled nor recovered after reception of the preamble signal in the conventional radio paging receiver. Accordingly, an error is liable to occur in the conventional paging receiver after reception of the preamble signal.